Studies have shown that transfer of the human cystic fibrosis transmembrane conductance regulator (CFTR) cDNA into cystic fibrosis (CF) epithelial cells corrects the defective cAMP-mediated chloride (Cl-) secretion that characterizes CF. However, no long term approach to somatic cell gene transfer has been developed. Gene transfer with an integrating vector such as retrovirus offers the exciting potential to provide long term correction. We hypothesize that pulmonary epithelial cell proliferation, stimulated by specific growth factors, will facilitate retroviral-mediated gene transfer with murine leukemia virus (MuLV) based vectors and result in long term expression. In 4 specific aims we will: 1) define the cellular proliferative responses to the growth factors keratinocyte growth factor (KGF) and hepatocyte growth factor (HGF), alone and in combination, 2) determine if accessibility of MuLV amphotropic receptor is a limitation to gene transfer, 3) develop alternative strategies to infect airway epithelia with MuLV from the apical surface independent of the receptor, and 4) test the optimized retroviral system for gene transfer to airway epithelia for correction of the CFTR C1- transport defect. This stepwise investigative approach will allow us to test the feasibility of gene transfer to pulmonary epithelia with high titer retroviruses, and will provide important insights into retroviral receptor biology in this cell type. It is our goal to take advantage of this vector for lasting correction of CFTR deficiency.